brownbear,
The flaking and delamination of the inside frame rails is visable inside the inspection hole as viewed though the rear wheel well opening. ITs piled with at least 1/2 of rust flakes inside the tube. Idealy, it would make sence just to cut out sections of the frame and then weld in new sections. Alot less work. The back channels definatly need to be removed as thay are also delaminated at the boundry layer and look like a telephone book

Where can I get these back channels? I know of somone in Colorado that has some good 60 parts. BTW your truck looks great. Did you have any holes in the wheel wells also?
All I know is I need to do something about the body more then the frame some areas are being taken over by cancer and need to be cut out and replaced.